public class Circle extends shape {
    static double PI = 3.1415926;

    double area(double r) {
        return PI * r * r;
    }

    double perimeter(double r) {
        return 2 * PI * r;
    }

    String toString(double r) {
        return "半径为:" + String.valueOf(r)
                + "的圆面积为:" + String.valueOf(area(r))
                + "周长为:" + String.valueOf(perimeter(r));
    }
}
